﻿/*
Copyright 2017 Google Inc

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

using System;
using System.Collections.Generic;
using System.IO;
using System.Threading;
using System.Threading.Tasks;

using Google.Apis.Auth.OAuth2.Flows;
using Google.Apis.Util.Store;

namespace Google.Apis.Auth.OAuth2
{
    /// <summary>A helper utility to manage the authorization code flow.</summary>
    /// <remarks>
    /// This class is only suitable for client-side use, as it starts a local browser that requires
    /// user interaction.
    /// Do not use this class when executing on a web server, or any cases where the authenticating
    /// end-user is not able to do directly interact with a launched browser.
    /// </remarks>
    public class GoogleWebAuthorizationBroker
    {
        // It's unforunate this is a public field. But it cannot be changed due to backward compatibility.
        /// <summary>The folder which is used by the <see cref="Google.Apis.Util.Store.FileDataStore"/>.</summary>
        /// <remarks>
        /// The reason that this is not 'private const' is that a user can change it and store the credentials in a
        /// different location.
        /// </remarks>
        public static string Folder = "Google.Apis.Auth";

        /// <summary>
        /// Asynchronously authorizes the specified user.
        /// Requires user interaction; see <see cref="GoogleWebAuthorizationBroker"/> remarks for more details.
        /// </summary>
        /// <remarks>
        /// In case no data store is specified, <see cref="Google.Apis.Util.Store.FileDataStore"/> will be used by 
        /// default.
        /// </remarks>
        /// <param name="clientSecrets">The client secrets.</param>
        /// <param name="scopes">
        /// The scopes which indicate the Google API access your application is requesting.
        /// </param>
        /// <param name="user">The user to authorize.</param>
        /// <param name="taskCancellationToken">Cancellation token to cancel an operation.</param>
        /// <param name="dataStore">The data store, if not specified a file data store will be used.</param>
        /// <param name="codeReceiver">The code receiver, if not specified a local server code receiver will be used.</param>
        /// <returns>User credential.</returns>
        public static async Task<UserCredential> AuthorizeAsync(ClientSecrets clientSecrets,
            IEnumerable<string> scopes, string user, CancellationToken taskCancellationToken,
            IDataStore dataStore = null, ICodeReceiver codeReceiver = null)
        {
            var initializer = new GoogleAuthorizationCodeFlow.Initializer
            {
                ClientSecrets = clientSecrets,
            };
            return await AuthorizeAsync(initializer, scopes, user, taskCancellationToken, dataStore, codeReceiver)
                .ConfigureAwait(false);
        }

        /// <summary>
        /// Asynchronously authorizes the specified user.
        /// Requires user interaction; see <see cref="GoogleWebAuthorizationBroker"/> remarks for more details.
        /// </summary>
        /// <remarks>
        /// In case no data store is specified, <see cref="Google.Apis.Util.Store.FileDataStore"/> will be used by 
        /// default.
        /// </remarks>
        /// <param name="clientSecretsStream">
        /// The client secrets stream. The authorization code flow constructor is responsible for disposing the stream.
        /// </param>
        /// <param name="scopes">
        /// The scopes which indicate the Google API access your application is requesting.
        /// </param>
        /// <param name="user">The user to authorize.</param>
        /// <param name="taskCancellationToken">Cancellation token to cancel an operation.</param>
        /// <param name="dataStore">The data store, if not specified a file data store will be used.</param>
        /// <param name="codeReceiver">The code receiver, if not specified a local server code receiver will be used.</param>
        /// <returns>User credential.</returns>
        public static async Task<UserCredential> AuthorizeAsync(Stream clientSecretsStream,
            IEnumerable<string> scopes, string user, CancellationToken taskCancellationToken,
            IDataStore dataStore = null, ICodeReceiver codeReceiver = null)
        {
            var initializer = new GoogleAuthorizationCodeFlow.Initializer
            {
                ClientSecretsStream = clientSecretsStream,
            };
            return await AuthorizeAsync(initializer, scopes, user, taskCancellationToken, dataStore, codeReceiver)
                .ConfigureAwait(false);
        }

        /// <summary>
        /// Asynchronously reauthorizes the user. This method should be called if the users want to authorize after 
        /// they revoked the token.
        /// Requires user interaction; see <see cref="GoogleWebAuthorizationBroker"/> remarks for more details.
        /// </summary>
        /// <param name="userCredential">The current user credential. Its <see cref="UserCredential.Token"/> will be
        /// updated. </param>
        /// <param name="taskCancellationToken">Cancellation token to cancel an operation.</param>
        /// <param name="codeReceiver">The code receiver, if not specified a local server code receiver will be used.</param>
        public static async Task ReauthorizeAsync(UserCredential userCredential,
            CancellationToken taskCancellationToken, ICodeReceiver codeReceiver = null)
        {
            codeReceiver = codeReceiver ?? new LocalServerCodeReceiver();

            // Delete token, which forces a user-interactive re-auth to occur.
            await userCredential.Flow.DeleteTokenAsync(userCredential.UserId, taskCancellationToken).ConfigureAwait(false);

            // Create an authorization code installed app instance and authorize the user.
            UserCredential newUserCredential = await new AuthorizationCodeInstalledApp(userCredential.Flow,
                codeReceiver).AuthorizeAsync
                (userCredential.UserId, taskCancellationToken).ConfigureAwait(false);
            userCredential.Token = newUserCredential.Token;
        }

        /// <summary>
        /// The core logic for asynchronously authorizing the specified user.
        /// Requires user interaction; see <see cref="GoogleWebAuthorizationBroker"/> remarks for more details.
        /// </summary>
        /// <param name="initializer">The authorization code initializer.</param>
        /// <param name="scopes">
        /// The scopes which indicate the Google API access your application is requesting.
        /// </param>
        /// <param name="user">The user to authorize.</param>
        /// <param name="taskCancellationToken">Cancellation token to cancel an operation.</param>
        /// <param name="dataStore">The data store, if not specified a file data store will be used.</param>
        /// <param name="codeReceiver">The code receiver, if not specified a local server code receiver will be used.</param>
        /// <returns>User credential.</returns>
        public static async Task<UserCredential> AuthorizeAsync(
            GoogleAuthorizationCodeFlow.Initializer initializer, IEnumerable<string> scopes, string user,
            CancellationToken taskCancellationToken, IDataStore dataStore = null,
            ICodeReceiver codeReceiver = null) =>
            await AuthorizeAsync(initializer, scopes, user, usePkce: true, taskCancellationToken, dataStore, codeReceiver).ConfigureAwait(false);

        /// <summary>
        /// The core logic for asynchronously authorizing the specified user.
        /// Requires user interaction; see <see cref="GoogleWebAuthorizationBroker"/> remarks for more details.
        /// </summary>
        /// <param name="initializer">The authorization code initializer.</param>
        /// <param name="scopes">
        /// The scopes which indicate the Google API access your application is requesting.
        /// </param>
        /// <param name="user">The user to authorize.</param>
        /// <param name="usePkce">
        /// If true, PKCE will be used by the authorization flow. Note that using PKCE is recommended for security reasons.
        /// See https://developers.google.com/identity/protocols/oauth2/native-app for more information.
        /// </param>
        /// <param name="taskCancellationToken">Cancellation token to cancel an operation.</param>
        /// <param name="dataStore">The data store, if not specified a file data store will be used.</param>
        /// <param name="codeReceiver">The code receiver, if not specified a local server code receiver will be used.</param>
        /// <returns>User credential.</returns>
        public static async Task<UserCredential> AuthorizeAsync(
            GoogleAuthorizationCodeFlow.Initializer initializer, IEnumerable<string> scopes, string user, bool usePkce,
            CancellationToken taskCancellationToken, IDataStore dataStore = null,
            ICodeReceiver codeReceiver = null)
        {
            initializer.Scopes = scopes;
            initializer.DataStore = dataStore ?? new FileDataStore(Folder);

            var flow = usePkce ? new PkceGoogleAuthorizationCodeFlow(initializer) : new GoogleAuthorizationCodeFlow(initializer);
            codeReceiver = codeReceiver ?? new LocalServerCodeReceiver();

            // Create an authorization code installed app instance and authorize the user.
            return await new AuthorizationCodeInstalledApp(flow, codeReceiver).AuthorizeAsync
                (user, taskCancellationToken).ConfigureAwait(false);
        }
    }
}
